4.1 INTRODUCTION

{A}

The user must keep in mind that much is still unknown about the over-all,
long term effects of various space environments on performance capabilities.
The data included here were derived from past experience with high-performance
aircraft, and the relatively limited experience, particularly with respect
to long orbital stays, with past space programs. A lot of the information
in this chapter has been derived from one-g data to which trend information
from the sources cited above was applied. Although less than perfect
or complete data were compiled for this chapter, it is the best information
in this field known to exist at this time.

This chapter is based on the premise that designers and mission planners
will do a better job if they are familiar with the capabilities of the
people for whom they are designing. When people go into space their
performance capabilities may change in important ways. The purpose of
this chapter is to document these changes.

The voluminous data that exists on human performance capabilities under
1-G (Earth) conditions are not included here. This material is covered
in other sources (see refs.
4, 19,
143, and especially 336).

4.2 VISION

{A}

4.2.1 Introduction

{A}

This section discusses aspects of visual performance that are, or are
likely to be, modified by space travel. For more general information
on vision, consult the references provided in
Paragraph 4.1.

4.2.2 Vision Design Considerations

{A}

Space-related factors that may affect visual perception as listed below.

a. Acceleration - The effects of acceleration on vision depend on the
direction of the force vector.

1. +Gz acceleration (eyeballs down) results in dimming of vision, followed
by tunnel vision loss of sight which begins on the periphery and gradually
narrows down until only macular (central) vision remains. This is followed
by total blackout and then loss of consciousness.

2. +Gx acceleration (eyeballs in) results in loss of peripheral vision.
This typically occurs at slightly over 4-G (based on a rate of onset
of 1-G per second). Complete loss of vision varies between individuals,
and with physical conditioning, training, and experience.

3. -Gz acceleration (eyeballs up) results in diminished vision, red-out
(red vision), an increase in the time for the eyes to accommodate, and
a blurring or doubling of vision.

5. Visual reaction time may be defined as the interval between the
onset of a stimulus and the initiation of the crewmember's response.
This interval is, in general, lengthened by increased G level.

6. Visual tracking is moderately degraded by increased G level.

b. Vibration - If vibration is sufficiently severe, visual performance
will be degraded. The severity depends on the frequency and amplitude
of the vibration along with the resonance frequency of the body part
involved. Unfortunately, the times when vibration is most likely to
be encountered (e.g., liftoff and landing) also tend to be times when
vision is important. Displays that must be read during projected periods
of high vibration should be designed accordingly. Design techniques
to be considered should include display characters which are sufficiently
large to be perceived even when blurred and sufficient illumination
to avoid scotopic vision which results in a lower Critical Flicker Fusion
Frequency.

c. Light in Space - Differences in light transmission and reflectance
in space result in some significant differences in available perceptual
cues in the extravehicular environment as compared to earth atmosphere.

1. Light Scatter - Atmospheric light scatter does not exist in space
due to the lack of particulate and gaseous material. Thus, aerial perspective
cues are absent. Figure-ground contrast is increased and shadows appear
darker and more clearly defined. Loss of these cues along with other
environmental consequences discussed below can degrade perception of
object shape, distance, location and relative motion.

2. Luminance Range (Contrast) - The extravehicular environment is marked
by a wider range of light intensities than normally encountered on Earth.
Shifting gaze from a brighter to a substantially dimmer scene will require
time for the eyes to adapt to the lower light level. For example, problems
arise on EVA missions when crewmembers go from working in sunlight to
working in shadows.

In Figure 4.2.2-1, adaptation time requirements
are shown for shifting gaze from a brighter to a dimmer environment.
For comparison, Figure 4.2.2-2 indicates
luminance values for some typical visual stimuli.

1. Absence of a Fixed Vertical Orientation - Recognition of familiar
objects, faces, and areas (e.g., workstation) is poor when viewed from
an orientation significantly different from the established vertical.
The viewer must be oriented within approximately 45 degrees of this
vertical to perceive the surroundings in a relatively normal fashion.
This fact argues for the establishment of a local vertical for each
living and working area within a space module.

2. Absence of Fixed Horizon and its accompanying foreground and background
cues can be expected to degrade extravehicular perception of object
shape, distance, location and relative motion.

3. Absence of a fixed, overhead sun position and its effects on shadow
cues is expected to have similar effects as those in 2 (above).

e. Light Flashes - The perception of light flashes has been reported
by many crewmembers during periods of darkness at specific orbital locations.
The cause is thought to be cosmic rays and/or heavy-particle radiation
traversing the head or eyes and triggering a neural response that results
in these perceptions.

f. Potential deficits - While visual perception in space is normal
in many respects, there are reports of various changes in vision (some
of them contradictory) that point out the complex consequences of the
above factors. These include Soviet reports of a shift in perceived
colors and a reduction in contrast sensitivity, along with a seemingly
contradictory report indicating improved visual acuity for distant objects.
Some U.S. astronauts have indicated a reduction in near acuity with
no apparent change in far acuity, while some crewmembers who wear reading
glasses on Earth found they were more dependent on them while in space.
Clearly, more research is needed before we can say more about these
effects.

4.3 AUDITORY
SYSTEM

{A}

4.3.1 Introduction

{A}

There is no evidence that human auditory functioning changes in space.
However, there are several factors (e.g., the effects of noise) that
should be considered in designing the space habitat.

g. Psychological Factors - The level of annoyance that noise produces
depends on a number of factors. Sensitivity varies greatly among individuals.

1. People are generally less sensitive to noise related to their well-being.

2. People are more sensitive to unpredictable noise.

3. People are more sensitive to noise they feel is unnecessary.

4. People who are most sensitive to noise become increasingly disturbed
as the noise persists, whereas the annoyance level of less sensitive
individuals remains constant over time.

5. The perceived abrasiveness of certain sounds is subjective and varies
considerably among individuals (e.g., consider the potential conflict
between opera and rock music lovers).

h. Cabin Pressure - Reduced cabin pressure causes a reduction in sound
transmission. This means that crewmembers have to talk louder to be
heard which can potentially lead to hoarseness on the part of some crewmembers.
The problem becomes more noticeable as the distance between individuals
increases.

4.3.2.2 Noise Design Considerations

Noise can have many adverse effects on humans and must be considered
when designing the human habitat. Considerations include:

a. Extreme Noise - Extreme noise can cause pain and temporary or permanent
hearing loss. The adverse effects of pure tones occur at a level about
10 dB lower than for broad band noise.

b. Extended Exposure - Exposure to loud noise for extended periods
of time can cause permanent hearing loss. The degree of exposure that
will result in damage depends on intensity and individual susceptibility.

4.4 OLFACTION
AND TASTE

{A}

4.4.1 Introduction

{A}

Changes in our senses of smell and taste might occur in space. These
changes are described below.

4.4.2 Olfaction and Taste Design Considerations

{A}

4.4.2.1 Olfaction

{A}

Aspects of olfaction (smell) that could influence design are presented
below.

a. Decreased Sensitivity - There are frequently reported problems with
nasal congestion while living in the microgravity environment.

b. Adverse Effects - Unpleasant odors have been associated with a number
of medical symptoms including nausea, sinus congestion, headaches, and
coughing. Such odors also contribute to general annoyance.

c. Microgravity Odors - Because particulate matter does not settle
out in a weightless environment, odor problems in a space habitat may
be more severe than under similar Earth conditions. Circulation and
filtering will influence the extent of the problem.

d. Visual Cues and Odors - Responses to odors can be accentuated by
the presence of visual cues. This increased responsiveness applies to
pleasant and unpleasant odors and is something that a designer could
potentially put to good use.

4.4.2.2 Taste

{O}

Generally there is a decrement in the sense of taste in microgravity.
This is probably caused by the upward shift of body fluids and accompanying
nasal congestion. Reports indicate that food judged to be adequately
seasoned prior to flight tasted bland in space. Given the important
role that food is likely to play in maintaining morale on extended space
missions, attention should be paid to this problem.

4.5
VESTIBULAR SYSTEM

{A}

4.5.1 Introduction

{A}

Microgravity results in two categories of vestibular side effects:
spatial disorientation and space adaptation syndrome (space sickness),
both of which can impair crewmember performance.

4.5.2 Vestibular System Design Considerations

{O}

4.5.2.1 Spatial Disorientation

{O}

Spatial disorientation is experienced by some crewmembers and should
be considered in the design of hardware and the planning of missions.

a. Spatial Disorientation - Responses include postural and movement
illusions and vertigo. For example, stationary crewmembers may feel
that they are tumbling or spinning. These illusions occur with the eyes
open or closed.

b. Frequency of Occurrence - The percentage of crewmembers who experience
spatial disorientation varies from mission to mission, but averages
approximately 50%. The conditions that determine the likelihood and
intensity of this disorientation are not well understood.

c. Duration - Some crewmembers may experience spatial disorientation
for the first 2 to 4 days of a mission.

d. Activity Schedule - While spatial disorientation need not cause
any serious problems, it is advisable not to schedule activities that
depend heavily on spatial orientation early in a mission.

4.5.2.2 Space Adaptation Syndrome

{O}

Aspects of space adaptation syndrome (SAS) relevant to the design of
space modules and mission planning are presented below.

a. Symptoms - SAS symptoms range from stomach awareness and nausea
to repeated vomiting. Symptoms also include pallor and sweating.

b. Incidence and Duration - It appears that approximately 50% of the
crewmembers are affected by SAS. Symptoms last for the first 2 to 4
days of flight.

c. Performance Decrements - A highly motivated crewmember may be able
to maintain a high level of performance despite the presence of mild
SAS. However, if motion sickness is severe, some crewmembers will be
unable to work until the symptoms lessen.

d. Cause - The leading theory as to the cause of SAS is the sensory
conflict theory. This theory states that space sickness occurs when
patterns of sensory input to the brain from different senses (vestibular,
other proprioceptive input, vision) are markedly rearranged, at variance
with each other, or differ substantially from expectations.

e. Volume Effects - The severity of SAS tends to increase as the motion
which induces sensory conflict and sickness (particularly head movements
in the pitch and roll modes) increases. It follows then that as the
volume in which a crewmember is working becomes larger, the chances
for this sickness inducing motion increases.

f. Space and Motion Sickness - It is assumed that the mechanism of
SAS and 1-G motion sickness are similar, but are similar, but it is
not possible to predict an individual's susceptibility to space sickness
from their susceptibility to Earth motion sickness.

g. Space Sickness Countermeasures.

1. Drugs - Anti-motion sickness pharmaceuticals (usually Scopedex)
have reduced the severity of SAS symptoms for some crewmembers, but
have appeared to be ineffective for others. It is likely that they would
be more universally effective if they were administered prophylactically,
either by injection or orally. The drug should be taken before symptoms
develop and absorption from the gut is severely hampered due to the
cessation of propulsive motions of the stomach., If a swallowed drug
becomes trapped in the stomach, little absorption will take place.

2. Head movements - In some cases restricting head movements has been
found effective in reducing the incidence of, and ameliorating the symptoms
of, space motion sickness.

4.6 KINESTHESIA

{A}

4.6.1 Introduction

{A}

Kinesthesia is the sense mediated by end organs located in muscles,
tendons, and joints, and stimulated by body movements and tensions.
Present knowledge of kinesthetic changes occurring when one enters microgravity
is limited to estimation of mass and limb position sense.

4.6.2 Kinesthetic Design Considerations

{O}

One experiment has indicated that some kinesthetic sensitivity degradation
occurs for a few crewmembers. The indications of this experiment are
provided below.

a. Mass Versus Weight - In a weightless environment, increments in
mass must be at least twice as large as weight increments in a 1-G environment
before they can be discriminated (see Figure
4.6.2-1).

b. Barely Noticeable Differences - For two masses to be perceived as
different under microgravity conditions, they must differ by at least
10% (see Figure 4.6.2-1).

c. Mass and Acceleration - Differential sensitivity for mass under
microgravity conditions can be improved by increasing the acceleration
force imposed on the object.

d. Mass Estimation - Absolute judgments of mass tend to be lower under
microgravity than under 1-G.

4.7 REACTION
TIME

{A}

4.7.1 Introduction

{A}

There appears to be some slowing of reaction times in space, although
little precise data are available.

The subject of this Section is Response Time. This time period consists
of two phases: 1) Reaction Time which is the time between the presentation
of a stimulus to a subject and the beginning of the response to that
stimulus, and 2) the time during which the actual response to the stimulus
is accomplished. It is believed that this section is actually referring
to Response Time and the titles and references should be changed accordingly.
However, Reaction Time should not be slowed in micro-gravity as it has
more to do with motivation and the effects of microgravity on the subject's
physiological and emotional states. A good definition of the difference
between Response Time and Reaction Time would help in the solution of
this dilemma.

4.7.2 Reaction Time Design Considerations

{O}

Information on reaction time that should be considered by designers
is provided below.

a. Object Mass - The time required to move an object in microgravity
increases as the mass of the object increases.

b. Control Operation - In microgravity, the speed of operating switches
(pushbuttons, toggles, rotary switches) is significantly lower than
in the 1-G condition.

(Refer to Reference 171
for more information on visual reaction times; and Reference 347,
for 1-G muscular-reaction time information.)

4.8 MOTOR SKILLS
(Coordination)

{O}

4.8.1 Introduction

{O}

There is a minor impairment of motor skills upon first entering microgravity.
This decrement is reduced or eliminated after a short period of adaptation.

4.8.2 Motor Skills (Coordination) Design Considerations

{O}

Aspects of human motor skills in space that should be considered by
individuals designing for space are provided below.

a. Adaptation Period - Motor skills are somewhat affected when crewmembers
are first exposed to microgravity, although these effects tend to diminish
or disappear with adaptation. During the period that the crew is adapting
to microgravity, fine motor movements are more adversely affected than
either medium or gross motor movements. Designers should minimize requirements
for crewmembers to exercise fine motor control early in the mission.
Switches should be easy to manipulate and care should be taken to preclude
accidental activation.

During periods that motor coordination is adapted for the micro-g environment,
short returns to an altered g-state (as in reentry, maneuvers, landings,
etc.) may result in dyskinesia and dysmetria. This can cause undershooting
when reaching for switches for buttons or applying force to control
sticks, pedals, knobs, handles, etc.

b. Postural Changes - A change in body posture in microgravity results
in a change in the relative position of body parts and can cause decrements
in coordination until adaptation occurs. Changes in body posture result
from the crewmembers assuming the increase in height due primarily to
spinal column expansion.

Refer to Section 3, Anthropometric and
Mobility, for additional information on microgravity posture.

c. Body Part Weight - When moving in microgravity, the muscular system
does not have to compensate for the weight of body parts. This changes
the muscular forces required for coordinated movement and requires the
system to readapt.

d. Large Mass Handling - When properly planned, no difficulty has been
encountered by crewmembers in moving large masses in a microgravity
environment.

4.9 STRENGTH

{A}

4.9.1Introduction

{A}

Physical work can be divided into two parts: power and endurance (anaerobic
and aerobic performance).

The next section addresses the first of these (power), and how it can
influence the design of facilities and equipment to achieve optimal
crewmember performance. (Endurance is addressed in Paragraph 4.10.2a).

4.9.2 Strength Design Considerations

{A}

Aspects of human strength that should be understood and considered
in designing for the space environment are presented below.

a. Strength - Strength is the ability to generate muscular tension
and to apply it to an external object through the skeletal lever system.
Sheer muscle mass (thus, body size) is a significant factor, with cross-sectional
area of the muscle fibers being a major determinant of the maximum force
that can be generated. Maximum muscular force (strength) can be exerted
for only a few seconds.

b. Muscular Endurance - Muscular endurance is the duration a submaximal
force may be held in a fixed position (Isometric), or the number of
times a movement requiring a submaximal force may be repeated (Isotonic).
The duration that a fixed percentage of maximum can be held is reasonably
constant across individuals.

c. Counterforces - Microgravity does not have certain counterforces
that allow people to effectively perform physical work in 1-G. Traction
which depends on body weight is absent, as are forces that result from
using body weight for counterbalance.

d. Working While Restrained - Crewmembers'
work capabilities while restrained can approach the efficiency experienced
on Earth-based tasks, but only where workstation design (including fixed
and loose equipment) and task procedures are optimized for the microgravity
environment.

e. Working Without Restraints - Without proper restraints, a crewmember's
work capabilities will generally be reduced and the time to complete
tasks increased.

f. Improved Performance - There are situations where a crewmember can
achieve improved strength performance in microgravity. These situations
occur when the crewmember uses the greater maneuverability of microgravity
to achieve a more efficient body position to be able to push off solid
surfaces.

g. Deconditioning - Experience in space indicates that both the strength
and aerobic power of load bearing muscles in crewmembers decreases during
missions exposing them to microgravity. Exercise programs have been
used to counter these deficits but to date have been only partially
effective.

h. Kinematics - The linear motion of free-floating crewmembers can
be described by relatively simple equations. The time crewmembers can
exert force is governed by the distance they can push before losing
physical contact. The force exerted during this time will typically
vary as in Figure 4.9.2-1.

The important aspects of this curve are the impulse (Fdt, or the area
under the curve), which will determine departure velocity; and the peak
force, which will determine peak acceleration. In the simplest case,
for a subject of mass m, an impulse I with a peak force F acting through
the subject's center of mass will result in a velocity

v = I/mwhere v is in ft/x, I is in lbfs,
and m is in slugs; or v is in m/x, I is in Ns, and m is in kg and a
peak acceleration

a=F/m where a is in ft/s2, F is in lbf,
and m is in slugs; or a is in m/s2, F is in N, and m is in kg.

In reality, of course, an impulse will rarely go exactly through the
center of mass to produce pure linear motion. For any offset of the
force from the center of mass, a percentage of the impulse will go toward
producing angular (tumbling) motion, with a corresponding decrease in
linear velocity. This percentage depends on the offset distance and
the subject's moment of inertia. (Moment of inertia varies considerably
with body position, and so is difficult to analyze parametrically, but
there will be some tumbling in practically all cases.)

Figure 4.9.2-2 shows the time that a
particular force can be exerted as a function of the magnitude of the
force exerted, the mass of the individual, and the distance pushed.
The velocity that the crewmember will have as they lose contact with
the surface is also given.

c. Male/Female Muscular Strength - Figure
4.9.3-5 provides a comparison of male and female muscular strength
for different muscle groups. These data allow a more accurate extrapolation
from male to female strength data than is provided by the old method
of assuming females have two thirds the strength of men.

(Refer to Reference 16
for more detailed male/female comparison data.)

d. Static Push Force - Maximal static push forces for adult males are
shown in Figure 4.9.3-6. While these
data were collected in a 1-G situation, the fact that they do not depend
on friction resulting from body weight makes them applicable to microgravity.
Corrections will have to be made for females (see
Figure 4.9.3-5).

e. Leg Strength - Leg strength for the 5th percentile male as a function
of various thigh and knee angles is reported in
Figure 4.9.3-7. Estimates of female leg strength can be made from
these data using the correction factors provided in
Figure 4.9.3-5.

Figure 4.9.3-5 Comparison
of Female vs. Male Muscular Strength

Note:

Female strength as a percentage of male strength for different
conditions. The vertical line within each shaded bar indicates
the mean percentage difference. The end points of the shaded bars
indicate the range.

(1) Height of the center of the force plate - 200 mm (8 in.)
high by 254 mm (10 in.) long - upon which force is applied. (2)
Horizontal distance between the vertical surface of the force
plate and the opposing vertical surface (wall or footrest, respectively)
against which the subject brace themselves.

*Thumb-tip reach - distance from backrest to tip of subjects
thumb as thumb and fingertips are passed together.

**Span - the maximal distance between a persons fingertips as
he extends his arms and hands to each side. (3) 1-g data

4.10 WORKLOAD

4.10.1Introduction

This section covers workload considerations including aerobic power,
aerobic endurance, and aerobic efficiency, as well as design factors
such as optimum workload, task selection, and task complexity.

4.10.2 Workload Design Considerations

{A}

Workload related factors that should be considered when designing for
optimum crewmember performance are presented below.

a. Endurance (Aerobic Power) -
Two complex factors determine the limits of an individual's capacity
to produce work and generate the requisite power. One of these is the
capacity to sustain output over a period of time (this is a function
of aerobic power). The second is strength (discussed in
Paragraph 4.9).

1. Aerobic power - Aerobic power is the total power that an individual
generates. It is related to usable power output by an efficiency factor
(see 5" below). Aerobic power is expressed as volume of oxygen
used per unit time. It is also commonly expressed in food calories oxidized
per unit time, when referring to workload for a given task.

2. Resting metabolic rate - At rest (zero external workload), the ratio
of oxygen consumed to body mass has been found to be quite consistent
across individuals [3.5 mL/kg/min (0.1 in3/lb/min)] and is called the
resting metabolic rate or 1 MET.

3. Maximum aerobic power - An individual's maximum aerobic power can
range from two times the resting rate for an invalid to 23 times for
a champion marathon. The average person will have a maximum aerobic
power of 8 to 12 times resting metabolic rate. As with rest, the energy
demands for a given workload are reasonably consistent across individuals.
Thus, their ability to perform becomes a function of the ratio of their
capacity to the demand.

4. Aerobic endurance - Aerobic endurance is a function of the individual's
maximum aerobic power, and determines how long an individual can perform
tasks of moderate to heavy intensity. Maximum effort can be maintained
for only a few minutes, while up to 40% of maximum can be maintained
over an 8-hr work shift with typical rest breaks (see
Figure 4.10.2-1). Most people would judge work requiring 40% of
their maximum aerobic capacity as moderate to heavy, but tolerable for
8 hours. Tasks that may be performed by any of a number of crewmembers
should keep metabolic energy requirements 10 to 20% lower than that
which would be considered tolerable by the least fit of the users.

Figure 4.10.2-1
Aerobic endurance: Duration and Workload

Percent of individual's
VO2 max

Duration2

Crewmember mass3

28 mL/kb/min
kcal/hr4 (Btu/hr)

42 mL/kb/min
kcal/hr4 (Btu/hr)

56 mL/kb/min
kcal/hr4 (Btu/hr)

100

5 min

54

454 (1800)

680 (2700)

907 (3600)

74

622 (2470)

932 (3700)

1243 (4930)

90

30 min

54

409 (1620)

621 (2470)

815 (3240)

74

560 (2220)

839 (3330)

1119 (4440)

80

60 min

54

363 (1440)

544 (2160)

726 (2880)

74

498 (1980)

746 (2960)

994 (3950)

50

3.5 hr

54

227 (900)

340 (1350)

454 (1800)

74

311 (1230)

466 (1850)

622 (2470)

40

8.0 hr

54

182 (720)

272 (1080)

363 (1440)

74

249 (990)

373 (1480)

497 (1970)

Notes:

1. Vo2 = aerobic power (consumed volume of O2
per unit time)
Exemplary fitness levels:
28 mL/kg/min (0.78 in3
/lb/min) would be considered "fair" for the general
female population and is below the average of the U.S. female
astronauts selected to date.
42 mL/kg/min (1.16 in3
/lb/min) would be considered "average" for males and
approximates the average for the U.S. male astronauts selected
to date.
56 mL/kg/min (1.55 in3
/lb/min) would be considered "high" for the males and
is well above average for the U.S. male astronauts selected to
date.

2. Nominal durations that individuals can maintain aerobic power
levels as percent of their maximums. Durations greater than one
hour normally require 10 minutes rest per hour, greater than 4
hours, a "lunch (rest) break" of approximately one hour.

5. Aerobic efficiency - In a shirtsleeve environment on Earth, human
efficiency ranges from approximately 35% to below 10%, depending on
specific movement patterns. In cycling, for example, the human has an
efficiency of about 21%. Thus, the useful power output for an individual
expending 500 kcal/hr cycling would be 122 W rather than the 581 W that
would result from 100% efficiency. Most of the wasted energy results
in metabolic heat that must be dissipated by the person.

b. Optimum Workloads - It is important to try to maintain work loads
that are close to optimum for each individual. This is especially true
on longer duration flights. Optimum work loads mean not only to avoid
overloading the individual but also not to underload them. Both of these
conditions have been shown to lead to decreased performance.

c. Biomedical Changes - Biomedical changes, such as diminished musculoskeletal
strength and reduced cardiac activity, can adversely affect work capacity.
In-flight decrements in exercise capacity approaching 10% have been
observed in some astronauts. These effects are likely to be more severe
on longer missions and should be controlled to the extent possible by
in-flight countermeasures such as exercise and diet.

d. Workload Prediction - It should be noted that a preponderance of
evidence from previous flight experience implies several mechanisms
which contribute to the difficulty of predicting workloads and task
times during missions. These mechanisms include:

1. Effects of Space Adaptation Syndrome. These tend to increase task
times due to the tendency for affected crewmembers to limit head motions.
The effects are particularly evident during activation phases involving
unstowage and frequent movements within the spacecraft, and are less
evident with fully adapted crewmembers after the first few days in orbit.

2. Effects of Inappropriate Workstation Design - As noted in
paragraph 4.9.2.d, workstation design can either support or confound
task performance microgravity, with task difficulties ranging from slightly
easier to significantly more difficult than the same task performed
in one-g, depending on the success of the workstation design.

3. Proficiency Loss - Depending on the criticality of a task and its
occurrence within the mission timeline, the length of time since a particular
task was last performed in a training exercise may be significantly
greater than the time between training sessions leading up to launch.

4. Adaptation to Microgravity Operations - This is a steep but significant
learning curve associated with living and working in microgravity which
often results in greatly decreased task times for second and subsequent
performances of similar tasks as compared with the initial performance.

These mechanisms act independently and together to increase task times,
particularly during early portions of a mission. Designers and mission
planners should anticipate these changes and should allow for task time
increments of from 25% to 100% compared with one-g experience.

e. Task Complexity and Fatigue - Simple tasks can be performed effectively
at much higher levels of fatigue than more complex tasks. Thus, in designing
the daily schedules, it would be beneficial to place the complex tasks
during periods of least fatigue.

4.11 Effects
of Deconditioning

{A}

4.11.1 Introduction

{A}

4.11.2 Effects of Deconditioning Design Considerations

{A}

4.11.3 Effects of Deconditioning
Design Requirements

{A}

Figure 4.11.3-1 presents design requirements and constraints for accommodating
deconditioned crewmembers. In establishing these requirements, different
levels of conservatism were applied to normal, and to backup/contingency
activities. Activities normally required for safe return must assure
success for highly deconditioned crews. Activities associated with off-nominal,
low probability situations are based on more optimistic estimates of
crew capability. In applying these requirements, the following must
be observed:

a. Crew activities and implementation methods listed are not presented
as requirements, but as a catalog of candidates for which the crew may
be used if the associated requirements and constraints are met. If activities
or implementation methods not listed herein are intended, they must
be submitted to the emergency vehicle Project Office for approval and
subsequent incorporation into this document.

b. For design purposes, deconditioning effects are assumed significant
only during reentry and subsequent mission phases. For operations prior
to entry interface (0.2g), other sections of this document are to be
applied without derating for deconditioning.

c. All crewmembers will remain in their couches or seats appropriately
restrained, throughout reentry and landing. After landing, the crew
will not be required to leave their couches or seats or release their
restraints until the vehicle is upright. For nominal mission, post landing
activities must not require the crew to stand without assistance by
ground personnel.

d. The crew shall not be required to perform any tasks during transient
environments associated with parachute opening or disreefing, landing
retrorocket firing, or landing impact.

e. Not accommodated as used in Figure 4.11.3-1
specifies that the crew shall not be required to perform the activity.
This does not necessarily imply that the crew is not able to perform
the activity.